1. Field of the Invention
The present invention relates to the field of machine tools and in particular to modifications allowing the changing of parts to be machined while meeting the integration requirements needed more particularly in the use of a machine tool for high speed machining.
2. Discussion of the Background
Usually, the changing device called "palletization" is used for supplying machine tools with parts to be machined: the device brings the part to be machined on the machining tool machining station, the machine tool works the machining range then the machined part to be machined is retrieved and replaced by a new part to be machined for machining.
The known devices called "step by step" are very much adapted for production line machining and to the configuration for machining machine tools for mass production. These machines contain multi-spindle tool heads which ensure the realisation at a very high speed of a range of machining.
These machine tools being subject to constant improvement in speed and precision and due to the fact that more flexible, faster and more precise new mono-spindle machines are appearing, the known devices are difficult to adapt as it is essential in future that they become more flexible, faster and more precise. In fact, the increased flexibility of these machines brings, amongst others, a difference in machining time from one machine to another and the technical procedure of conveying "step by step" cannot be used in such a configuration.
Another constraint to which a changing tool device must now adapt is dry machining. In fact, dry machining, that is to say without liquid projection, does away with the common removal means of chips so that these chips are evacuated with more difficulty and become therefore a more important factor in seizing the components of the machine, of distorsion of the references and of malfunction.
The concept of rotary "palletization" devices in front of each machine and being used as interface between the classical conveying chain of the parts and a high speed machining machine tool, seems to be the best solution to the problem of flexibility. However, a disadvantage of these devices is the high free volume required, at the level of the machining station, by its installation, as the rotation of these devices requires a cylindrical volume of which the base would have for diameter the length of the pallet-changer, taking much more space than a classical palettizer in translatory motion. This disadvantage has often forced the tool office technicians to conceive less space-taking machining assemblies.
The problem of leaktightness, and in particular during dry machining, is more complex for rotary pallet-changers as they bring a pallet in a machining zone by a high speed rotating movement which is difficult to get leaktight, due to the fact that the entire surface of the pallet-changer resting on the machine tool becomes an obstacle at the time of the rotation of said pallet-changer. The leaktightness of existing devices, when it exists, is not always a satisfactory and acceptable compromise in view of the conditions required nowadays for very high speed machining.